The present invention generally relates to fuel storage apparatus and, more particularly, relates to a triple sheet thermoformed fuel tank with high performance aspects for use in light-duty vehicles.
It is well known in the art to provide fuel storage apparatus such as gas tanks to hold the fuel used by an engine adapted to propel a land vehicle. Two types of fuel tank are most common. A first type includes steel fuel tanks that generally comprise an upper shell half and a lower shell half joined by known manner to provide a steel storage fuel tank. The second type includes polymeric fuel tanks that are characteristically formed according to blow molding and, to a lesser extent, injection, and thermoform molding processes to provide a plastic fuel storage tank.
In the past decade, global steel fuel tank production has experienced a significant decline while polymeric fuel tanks have enjoyed exceptional growth. Although steel fuel tanks are durable, they are also heavy weight, which increases fuel consumption. Polymeric fuel tanks are lightweight, relatively low cost and can be readily molded into complex shapes for optimum space utilization. Worldwide tailpipe emission limits and other competitive influences have finally caused automobile manufacturers to use polymeric fuel tanks in ever-greater numbers.
Polymeric fuel tanks have problems. There are limitations imposed upon fuel tank apparatus by the molding equipment deployed for their manufacture. Improvements in the blow molding art are in particular required to meet new and more stringent light-duty vehicle emission limits. For example, fuel tank vapor emission limits represent new areas of heightened concern. The permeability of blow-molded fuel tanks has led some automobile manufacturers to reconsider the potential low permeability of hydro-formed steel fuel tanks to meet the more stringent fuel tank emission limits.
Several potential areas of evaporative emission characterize fuel tanks. A first area of concern is permeability at a seam between two fuel tank halves in the case of steel and thermoformed fuel tanks, and along any seams of a blow-molded fuel tank. A second area of concern is emission at the openings at the tank interface with the external and internal fuel system components. The fuel system components generally include a Filler Pipe Assembly, a Vapor Control System, Engine Fuel and Vapor Lines, and a Sender Unit. Each of these fuel system components itself comprises an array of complex sub-components.
The first problem area of permeability at a seam is greater in steel and thermoformed plastic fuel tanks than in blow molded fuel tanks. The art of blow molding is characterized by the expansion of a stream of thermoplastic within a hollow mold, as characterized by Boechker in Publication No. 2001/0013516 A1. The blow molding process yields a substantially seamless body. Multi layered streams of blow-molded plastic are also used for several aspects principally including impermeability.
Seams are unavoidable characteristics of both steel and thermoformed plastic fuel tanks. Both processes contemplate the uniting of two fuel tank halves. The steel fuel tank industry is decreasing emissions at the seam with improved welding, adhesive, gasket, and coating technologies. The steel industry is also experimenting with steel blow molding. Thermoformed fuel tanks are now preferably composed of composite sheets that possess interior layers of non-permeable polymeric material, as set forth in International Publication No. WO 00/43230 to Sadr or U.S. Publication No. 2001/0045433 to Ellis. The composite sheet is co-extruded in known manner. The barrier layers are substantially thermally bonded together in a twin-sheet compression phase to provide a near non-permeable seam. Thus, permeability at the seam is less of a problem today than in the past.
The second problem area of permeability at interfaces between a fuel tank and its fuel system components has lead to several advancements in polymeric fuel tanks in particular. For example, many of the fuel system components are integrated into the tank itself to reduce the number of openings and connections that contribute to fuel tank emissions. This approach is known as Ship-in-a-Bottle, and has been readily practiced in the steel fuel tank sector for some time. The Ship-in-a-Bottle (SIB) technique is particularly amenable in the thermoforming process. The SIB approach is problematic for blow molding, as described by Boechker in Publication No. 2001/0013516 A1. The SIB amenability of thermoforming will result in a relative decline of blow molded and a relative increase of thermoformed fuel tanks in the coming years. Although SIB has been demonstrated by technologically advanced blow molding practitioners, over-all economic factors favor a shift toward increased global thermoformed fuel tank production because of the ease with which the SIB technique may be implemented.
The SIB technique has been adapted in recent years for a number of purposes. For example, in U.S. Pat. No. 6,138,859 to Aulph et al. an internal component-carrying cradle is adapted with baffle aspects that reduce the sloshing noises of moving fuel within the fuel tank. A cradle with baffle aspects and integral lines and connectors is also disclosed in Boechker in Publication No. 2001/0013516 A1.
The SIB method has been practiced in the thermoforming industry for many years. For example, Spencer Industries Incorporated of Dale Ind. provides an eight-page brochure showing a xe2x80x9cDoor-In-A-Doorxe2x80x9d refrigerator door wherein it is written xe2x80x9cDuring the twin sheet forming process, a three piece injection molded internal hinge assembly is inserted by means of a pick and place robotxe2x80x9d. In the present case, the pick and place robot is positioned exteriorly adjacent the form station of a four-station Brown twin sheet thermoforming machine.
In U.S. Publication No. 2002/0017745 to Vorenkamp et al. a hybrid thermoforming methodology is suggested providing a SIB function. Although it may be argued the thermoforming methodology is known in the art, such as in U.S. Pat. Nos. 3,779,687 to Alesi and 6,372,176 to Edendahl et al., the problem with the Vorenkamp method is that synchronization of two parallel lines would be problematic and far less productive, ultimately, than two conventional rotary style twin sheet thermoforming machines characteristic in the industry.
The cradle carrying the internal fuel system components is characteristically made of the same material as the inside walls of the fuel tank. The thermal plastic cradle may be fused in place within the fuel reservoir by compressing the cradle against a heated wall of the fuel tank in the process of twin sheet thermoforming, as in U.S. Pat. No. 6,138,859. Alternatively, an adapter for welding the cradle to the fuel tank wall may be attached to the cradle for this purpose as in Vorenkamp Publication No. 2002/0020487. A second method to locate a cradle within the fuel tank is with a combination of recesses and projections, for example, as in U.S. Pat. No. 6,176,260 to Hahner et al.
The described shift from blow molding to thermoforming has caused the blow molding industry to enjoin the threat posed by twin sheet thermoforming by advancing the art. For example, Schwochert in International Publication No. WO 00/48859 discloses a fuel tank with a molded polymeric cover providing a fuel vapor collection chamber. According to Schwochert""s method, the exteriorly visible fuel system components and body seams are enclosed with a polymeric cover by way of secondary operations thereby trapping any fuel vapors that may escape from the body seams and the connections of the fuel system components. According to this remedial approach, deployed blow molding machinery may be kept in service with the aid of such auxiliary intervention. One problem with the Schwochert approach concerns the bond between the cover and the complex tank body. It is anticipated that the cover itself will be difficult to bond to the polymeric fuel tank, which could result in unacceptable vapor leaks at the cover seam.
Although thermoforming is amenable to the Ship-in-a-Bottle advantage, thermoforming nonetheless is a relatively new fuel tank enabling technology and several problems have been identified. In particular, once the fuel system components have been enclosed within a twin sheet thermoformed structure, access for further manufacturing subassembly and in-field service and repair must be provided in order to implement a thermoformed fuel tank. As may be appreciated by referring to FIG. 3 of International Publication No. WO 00/74965, this is not a problem with blow molding techniques. The blow molding process can be readily adapted to provide threaded flange elements upon an exterior surface of the fuel tank body wherein the threaded flanges receive a removable cap or a developed cover for both assembly and service purposes.
In U.S. Pat. No. 6,179,145 B1 a thermoformed fuel tank with an inspection tower receiving a threaded sealing cover is suggested. Unlike International Publication No. WO 99/56977, which disclosed a similar approach for a blow molded fuel tank, there is no suggestion in ""145 as to how this approach can be reduced to practice by a thermoforming practitioner. Although means for accessing internal fuel tank components for repair and service are clearly suggested, the approach of ""145 is found wanting in several ways. In particular, the inspection tower is provided so a service port can be opened and then later sealed by an in-field repair technician. This methodology does not contemplate using a service port to finally assemble and connect the fuel system components to the fuel tank body in the manufacturing stage. Therefore, these sub-assembly operations must occur before the fuel tank halves can be joined together in secondary operations, such as by the suggested method of welding. The ""145 scheme eliminates the inherent advantage of joining the heated sheets in an instant twin-sheet forming phase, and using a threaded inspection tower opening as means to access, sub-assemble, connect, inspect, service and seal the fuel system components associated with a thermoformed fuel tank.
Thus, it may be appreciated through a review of the prior patent art and related non-patent publications that the thermoforming process provides several key advantages that may be readily adapted to thermoformed fuel tanks. These understood advantages include SIB, rapid twin sheet manufacture (a process which may be appreciated by referring to U.S. Pat. No. 3,925,140 to Brown), and the ready use of composite polymeric sheet with engineered properties. There are, however, several unknown thermoforming processes advantages that can be applied to fuel tank apparatus. It is therefore desirable to identify these unknown advantages so that the thermoforming art can be fully utilized as an enabling technology to provide high-performance fuel storage apparatus.
It is, therefore, one objective of the present invention to provide high-performance fuel storage apparatus for light-duty vehicles. According to this object, advanced thermoforming technologies are adapted to provide fuel tanks having at least three composite polymeric sheets.
According to this object, the fuel tank can be instantaneously thermoformed into a unitary article for a rapid production cycle. According to further aspects of this object, one or more composite polymeric sheets are provided enabling fuel tank improvements and enhanced functionality.
It is another object of the present invention to provide a fuel tank with at least two hollow sections between at least three composite polymeric sheets. According to this object, one or more hollow sections are provided yielding advanced fuel tank characteristics.
It is yet another object to provide one or more threaded elements upon at least one of the composite polymeric sheets forming a thermoformed fuel tank. According to an aspect of this object, the threaded elements enable post-forming sub-assembly operations to be completed most efficiently. Still according to this aspect, fuel system components are connected to threaded elements that may be readily serviced by in-field technicians.
It is still another object to utilize a plurality of engineered composite polymeric sheet of greater or lesser thickness in cross-section, along with filler rigidified substrates, vapor barrier layers, RF transparency, intumescent surfaces, improved thermal bonding enhancements as well as other features and aspects. According to this aspect, more economical, technically sophisticated and emissions compliant fuel tanks with high-performance features may be used in light-duty vehicles.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.